Public key cryptography is a security standard used over networks such as the internet. Public key cryptography is a form of assymetric key cryptography that includes a public key pair having a public key and a private key. As the name indicates, the public key is published to the public for anyone to use, and the private key is kept secret by a private key holder. Articles of information encrypted with the public key can only be decrypted by the private key. The private key can also be used to perform a cryptographic function called digital signing, that proves the authenticity of the signed data.
Many products and services offered on the internet require an individual to prove certain information before the product or service can be provided to a client. For example, to purchase alcohol online a user must first prove that he is 21 or over. To prove this, he must enter certain personal information such as his name, date of birth, and driver's license number. The amount of information that must be provided includes much more personal information than merely specifying whether or not the user is actually over 21. This extra information must be provided so that the web server that is selling the alcohol can verify that the user is over 21.